I think you must be thinking of something slightly different when you say gameplay than I am because for me the gameplay seems like it should be simple.

Cliff hexes should act just like chasm hexes but just look different. Flying units could stand on them but other units can't but since the unit is flying it sholdn't look that strange in combat.

"There are two kinds of old men in the world. The kind who didn't go to war and who say that they should have lived fast died young and left a handsome corpse and the old men who did go to war and who say that there is no such thing as a handsome corpse."